This invention relates to devices for detecting faults in alarm systems. In particular, it relates to a device for detecting faults in a closed loop burglar alarm circuit of the sort commonly installed in commercial buildings and residences.
A common form of burglar alarm system comprises a closed, low current DC loop. Within the loop are a variety of normally closed switches which are opened by the action, for example, of opening a window or opening a door that has been appropriately armed. The circuit may also include switches which are opened by pressure, as for example, pressure switches underneath rugs. After the installation of the burglar alarm system has been completed, there are often false alarms, e.g., actuation of the alarm as if one of the switches were open when, in fact, all of the switches are apparently closed. This frequently results from leakage current caused by loose connections, faulty switches or corroded components. It is difficult to determine the location of such faults since the leakage current involved may be too low to be observed by ordinary meters. Further, conventional or prior art devices to detect problems in alarm circuits are typically discontinuous so that one must continuously watch a meter to determine whethere there is any change in current when a suspected component is vibrated. Such constant watching of a meter is tedious and difficult and requires two persons to test the circuit.
One object of this invention is to provide a device to detect faults in a low current circuit without requiring the constant watching of a meter or the like.
Another object of the invention is to provide a device for detecting the faulty portions of an alarm circuit where faults involve changes of resistance of as low as one ohm.
Other objects and advantages of the present invention will be apparent from the description and claims which follow taken together with the appended drawings.